This invention relates to tufting machines and more particularly to apparatus for increasing the range of operation of a cam driven needle bar jogging device by extending the pattern repeat capabilities, i.e. the stitch capacity of a given size cam.
In the production of tufted fabrics it is known to jog or shift the needle bar transversely across the tufting machine relatively to the base material in order to create various pattern effects, to break up the unattractive alignment of the longitudinal rows of tufts and to reduce the affects of streaking which results from variations in coloration of the yarn, the latter difficulty being a result of variations in the dye absorbing property of heat set yarns.
Various devices have been proposed and are in use for controllably applying a step-wise force to the needle bar of the tufting machine in accordance with a pattern. For example, the primary means for supplying this jogging has been a pattern cam driven in timed relationship to the reciprocation of the needle bar and acting upon a cam follower mechanism coupled to the needle bar. Exemplary of this prior art device are U.S. Pat. Nos. 3,026,380 and 3,934,524. Because of the limited patterning capabilities of a cam, and especially the limited longitudinal pattern repeat, the cam providing a longitudinal repeat every revolution of the cam, prior art needle bar shifters having patterning capabilities beyond that provided by the cam and follower systems have been developed. Electrically/electronically programable systems proposed for replacing the cam driven systems are disclosed in U.S. Pat. Nos. 3,964,408 and 3,972,295, which utilize pawl and ratchet devices, U.S. Pat. No. 4,010,700 which uses an indexing device, and U.S. Pat. No. 4,173,192 which uses a hydraulic actuator. A pneumatic actuation system has also been proposed recently and is the subject of copending U.S. application Ser. No. 245,377 filed Mar. 19, 1981 and assigned to the assignee of the present invention.
However, because of the greater reliability, simplicity and lower cost of a cam drive system vis a vis the known expanded pattern needle bar shifters, a cam driven system is still preferable to these others.
In a conventional cam driven needle bar shifter apparatus, the cam is rotatably driven through proper reducing apparatus from the main shaft of the tufting machine and rotates continuously. However, since the lateral shifting of the needle bar must occur only during that portion of the machine cycle when the needles are above the base fabric and needle plate so as to avoid interference between the needles and the needle plate, only a portion of the cam circumference is available for controlling the needle bar movement. The remaining portion of the cam circumference is of a constant radius and non-effective for patterning, it merely idles the needle bar. For example, normally the needle bar is shifted or jogged laterally during approximately 90 degrees to 120 degrees of the needle bar reciprocation cycle, this period corresponding to the period the needles are safely free of the needle plate without imposing excessive acceleration forces on the apparatus. Thus, in a conventional cam driven shifter approximately one quarter to one third of the circumference provides the pattern, with the remaining three quarters to two thirds of the circumference being merely an idle surface. If the surface of the cam is divided into sectors equal in number to the number of stitches in the pattern, the angular distance from a point in one sector to a similarly disposed point in an adjacent sector is the angle the cam must rotate for each revolution of the tufting machine shaft, i.e. for each cycle of the needle bar. Because of this, and because of the small surface available for a follower to ride upon each sector of a practical sized cam, the number of sectors into which the cam may be divided, and hence the number of stitches in a pattern produced by the cam, has been limited.